The invention relates to detachable thumb assemblies for construction machines. Such detachable thumb assemblies may be attached to the backhoe digging, apparatus of machines such as excavators or backhoe loaders, where they can be used in conjunction with a main implement mounted on said digging apparatus, such as an excavating bucket or a hammer.
Many construction equipment machines are equipped with a backhoe. A backhoe is a piece of equipment where a work implement, primarily a bucket, is mounted at the end of a digging apparatus, the apparatus being itself mounted on a chassis of machine. The digging apparatus usually comprises at least a boom, which is articulated to the chassis through at least around a horizontal axis, and very often also around a vertical axis, and a dipper which is articulated at the free end of the boom around another horizontal axis. The dipper may also be articulated with respect to the boom around a vertical axis. Each of these movements is controlled by a power cylinder, usually a hydraulic cylinder, respectively a boom cylinder for controlling the movement of the boom relative to the chassis and a dipper cylinder for controlling the movement of the dipper relative to the boom. The bucket is articulated to the dipper around another horizontal axis and is controlled by another cylinder. In a backhoe, the digging apparatus can be controlled to pull back material towards the chassis of the machine.
In some cases, the dipper part of the digging, apparatus is extendible, whereby it comprises a proximal part articulated to the boom and a distal part which is slidingly connected to the proximal part so as to form a length-adjustable dipper assembly. A cylinder is in most cases provided for adjusting the relative position of the two parts of the dipper. A slide mechanism is provided for connecting the two parts of the dipper in such a way that the two parts may slide relative one to the other along a longitudinal direction but that they are otherwise rigidly connected along all other directions. Of course, the work implement of the backhoe apparatus is then connected to the forward end of the distal part of the extendible dipper assembly.
In some cases, the proximal and distal parts are arranged so that, in cross-section, the distal part is essentially received within the proximal part, which can exhibit a hollow box cross-section. When the extendible dipper assembly is in a retracted position, only a forward extremity of the distal part emerges out of the proximal part, so as to be as compact as possible, thereby maximizing the length ratio of the assembly between its fully extended and fully retracted positions.
It is also known to provide the construction equipment machine with a detachable thumb assembly to be mounted on the machine's apparatus. Such an assembly is useful for grabbing material between the main work implement and said thumb, as the thumb is used in opposition to the other fingers in the case of a human hand. While some thumb assemblies have a fixed position with respect to the apparatus, or a position which can only be adjusted during, a non-use phase of the machine, many thumb assemblies provide a controllable thumb where the position of the thumb with respect to the digging apparatus may be adjusted during a work phase of the machine. Such control is most often governed by a hydraulic cylinder which extends between the apparatus and the thumb.
Document U.S. Pat. No. 4,375,345 discloses a detachable thumb assembly mounted on a non-extendible dipper. The assembly comprises a link which is pivotally connected to a pair of mounting plates. The thumb is pivotally connected to the mounting plates around the same axis as the link, said axis being offset from the bucket pivoting axis. The mounting plates engage a bucket pivot pin and a link pivot pin in an abutting relation. Attachment of the assembly is achieved by the link which engages a lower side of the dipper through an abutment portion and through a lock bolt. The thumb cylinder is connected to the link at its back end, while its rod front end is connected to the thumb, near the free end thereof.
Document U.S. Pat. No. 7,165,930 discloses a detachable thumb assembly comprising a mounting bracket which is to be mounted on the machine's digging apparatus through two dedicated pins which engage specific brackets. The thumb is articulated on the mounting bracket around a pivoting, axis which coaxial with the bucket/apparatus articulation axis, but the two articulations are physically separate inasmuch they do not share any component. The thumb cylinder is a conventional cylinder which is connected to the mounting bracket by its back end, so that the total length of the bracket is quite important relative to the length of the dipper assembly on which it is to be mounted.
It is desirable to propose new design of a detachable thumb assembly which is compact, both in terms of the total dimensions of the thumb assembly in itself and in terms of the total dimensions of the assembly when it is attached and operative on the machine's digging apparatus.
The invention provides for a detachable thumb assembly for a construction equipment machine, comprising                a mounting bracket for attaching the thumb assembly to a digging apparatus of the machine;        a thumb pivotally connected on the mounting bracket;        a thumb cylinder comprising a cylinder body connected to the mounting bracket and a cylinder rod which extends from a front end of the cylinder body and which is connected to the thumb, characterized in that the body of the thumb cylinder is pivotally connected to the mounting bracket at a connection portion of the body which is distinct from a body back end portion.        
The invention also provides for a backhoe digging apparatus for a construction equipment machine, said apparatus being equipped with such a thumb assembly.